Protein synthesis ceases in the red cells at the reticulocyte stage. Hence a progressive decline in metabolic capacities of the cell continues until metabolism in the cell reaches a level incompatible with survival. The progressive changes that accompany red cell aging will be evaluated by study of metabolic parameters in groups of cells of different mean age isolated by ultracentrifugation on discontinuous density gradients. Since the relationship between position of the cells in these gradients and mean age has been established by previous glycine 2-C14 dating experiments, this technique will permit quantitating rates of decline of age-dependent parameters. Decline of enzymatic activities will be measured: these will, however, only provide an indication of how potentialities for individual enzymes change with age. These studies will thus be integrated with measurement of level of intermediates and measurement of actual rates of utilization of intermediates in relationship to age of the cells. The latter will be obtained in hemolysates incubated in conditions where rates of production of lactate and lactate/glucose ratios are similar to those of intact cells. This study will analyze from different points of view the development of metabolic blocks and indicate whether the death of the red cell results from the decline in several concurrent metabolic steps or from one single rate limiting factor. The effect of decreased activity and change in kinetic characteristics with age will be studied in normals and G6PD deficient males. The inhibitory effect on the enzyme and the hemolytic effect on the cells of drugs known to induce hemolysis will be similarly evaluated in relation to the aging of the cells. Studies of the mechanism of G6PD deficiency (defective synthesis or unstable enzyme) will be continued on bone marrow and fibroblasts from individuals with different mutants associated with congenital non-spherocytic hemolytic anemia. Human subjects involvement will be limited to blood sampling. Purpose of sampling will be explicitly explained.